The present invention relates to a method for fabricating a semiconductor device, and more particularly, to a method for fabricating a hard mask and a method for forming a pattern using the hard mask.
As semiconductor devices have shrunken, line patterns such as gate lines and bit lines include a multiple-layer hard mask structure due to a lack of photoresist margin during etching and a lack of self-aligned contact margin during trench-defining.
FIG. 1 illustrates a cross-sectional view of a typical method for forming a pattern. An etch target layer 11 is formed, and a hard mask 12 including multiple layers is then formed. At this time, the hard mask 12 includes a stack structure configured at least with a bottom layer 12A and an upper layer 12B. The bottom layer 12A and the upper layer 12B include different materials.
A bottom anti-reflective coating (BARC) layer 13 is formed over the hard mask 12 to reduce scattering reflection during a photo-exposure process. A photoresist pattern 14 is then formed. Although not shown, the BARC layer 13 is etched using the photoresist pattern 14 as an etch barrier. The hard mask 12 and the etch target layer 11 are also etched to form a pattern.
However, the multiple-layer hard mask 12 may generate undesirable events in some patterns after the patterns are formed due to discordance between the bottom layer 12A and the upper layer 12B. In particular, a large amount of foreign substances may be generated when the hard mask 12 includes a tungsten layer and an amorphous carbon layer and the tungsten layer and the amorphous carbon layer are in direct contact with each other.
FIG. 2 illustrates a micrographic view of foreign substances generated after a pattern is formed. The foreign substances are generated by an abnormal non-uniform contact between a tungsten (W) layer and an amorphous carbon layer in a multiple-layer hard mask during an etch process. The foreign substances are formed on a surface of the tungsten layer.
The foreign substances are often not generated when one of the tungsten layer and the amorphous carbon layer is omitted. However, the hard mask including the tungsten layer and the amorphous carbon layer is used to increase a self-aligned contact margin when forming the pattern and when performing the self-aligned contact etch process for forming contact holes. Thus, it is generally difficult to omit one of the layers.